During the hydrogenation of aldehydes and ketones to alcohols the formation of acetals and ketals readily occurs if the hydrogenation is carried out below pH 7 or in the presence of solid catalysts comprising acidic centers. The acetals and ketals cannot be satisfactorily converted into the alcohols forming the basis and formed from the carbonyl compound by mild hydrogenation. Stable cyclic acetals and ketals, namely, 2-substituted 1,3-dioxolane- and 1,3-dioxan derivatives are produced in particular during the hydrogenation of .alpha.- and .beta.-hydroxycarbonyl compounds to 1,2- and 1.3-diols. In order to hydrogenate such acetals and ketals, rather high temperatures and/or special catalysts are required. One problem in reducing the content of acetals and ketals in aqueous, alcoholic reaction mixtures of differing provenance also resides additionally in the fact that there is a danger that the alcohol itself will be decomposed under the rather severe hydrogenation conditions required.
3-Hydroxypropionaldehyde is reduced to 1,3-propane diol in the method of EP-A 0 572 812 in which a first hydrogenation stage for the purpose of reducing the content of residual carbonyl is followed by a second hydrogenation stage at a pH of 2.5 to 6.5 at an elevated temperature. The same hydrogenation catalyst was used in both temperature stages, preferably a Pt/TiO.sub.2 -carrier catalyst and Ni/Al.sub.2 O.sub.3 /SiO.sub.2 -carrier catalyst. It was determined that only an unsatisfactory conversion can be achieved in the second stage with a noble metal catalyst on an oxide carrier, with a neutral or weakly acid pH range; in addition, the catalytic activity drops after a few hours of operation to a level which is lower than at the beginning.
According to WO 97/01523 cyclic diethers can be hydrogenolytically split with a 1,3-dioxo group in an aqueous phase in the presence of a metallic catalyst such as Ru on activated carbon at 100.degree. to 200.degree. C. at a pH of 1 to 6. According to the examples the degree of conversion is not quantitative. In particular, this document furnishes no suggestion for degrading small amounts of acetal or ketal in addition to large amounts of an alcohol without also decomposing the alcohol at the same time by hydrogenolysis. In addition, a very high ratio of catalyst to substrate is required in order to bring about the conversion. In a similar manner the hydrogenolytic splitting of 1,3-dioxan derivatives is incomplete if Raney nickel is used as catalyst, according to U.S. Pat. No. 4,044,059.
In order to reduce the carbonyl content of lauryl alcohol containing 0.1% by weight lauryl aldehyde by catalytic hydrogenation, nickel catalyst on kieselguhr diatomaceous earth is recommended as the catalyst according to the brochure "Carbonyl Removal from Oxoalcohols" (Engelhard Corp.) even though this company also supplies carrier-bound noble-metal catalysts. Nickel catalysts tend to leach metal at a pH below 7, which has a disadvantageous effect on the workup.
Ind. Eng. Chem. Res. 33 (1994), 566-574 teaches the degradation of organic components such as sugar and glycols in aqueous media hydrogenolytically in the presence of Ni catalysts or ruthenium on various oxide carriers. When using such catalysts to reduce the acetal content or ketal content in an aqueous medium containing an excess of an alcohol with respect to the amount of the acetal or ketal a partial degradation of the alcohol must be expected in the process described.